System and Method for a Battery and Test Circuit

ABSTRACT

According to an embodiment, a system includes a switching regulator and an electrochemical storage test circuit. The switching regulator is coupled to a power supply input and configured to supply a regulated voltage to a regulated supply terminal that is configured to be coupled to a device. The electrochemical storage test circuit is configured to be coupled to an electrochemical storage unit. The electrochemical storage test circuit includes a bidirectional switch with a first switch terminal coupled to the regulated supply terminal, a second switch terminal configured to be coupled to the electrochemical storage unit, and a switch control terminal. The electrochemical storage test circuit also includes a built-in self-test (BIST) circuit configured to be coupled to the electrochemical storage unit and to the switch control terminal.

TECHNICAL FIELD

The present invention relates generally to electronic systems, and, inparticular embodiments, to a system and method for a battery and TestCircuit.

BACKGROUND

Airbag supplemental restraint systems (SRS) have become increasinglypervasive because of their ability to protect vehicle occupants fromserious injury in the event of a collision. A typical airbag system hasan airbag, an inflation device, and a crash sensor that detects a suddendeceleration of the vehicle. In order to prevent accidental or unwantedairbag inflation, airbag systems generally require a high safetyintegrity level to prevent accidental or unwanted airbag inflation. Oneway to maintain a high safety integrity level is to use multiplesensors. For example, a typical side impact airbag system has a pressuresensor inside a car door, and an accelerometer located in a pillar nextto the car door. If the pressure sensor measures a sudden rise inpressure at the same time the accelerometer detects an acceleration, theSRS system deploys the side impact airbag. By setting proper timing andamplitude conditions for the pressure sensor and accelerometer, theairbag is deployed in the event of a collision, but not from a vibrationcaused by a person closing the door, for example. Generally, therequisite sensing and triggering of the airbag system is coordinated bya microcontroller or microprocessor coupled to various elements of theSRS system.

One issue related to the safety integrity of SRS is the electricalintegrity of the circuits and circuit boards that are coupled to the SRSsystem. This integrity is maintained, not only to the microcontrollerand components of the SRS system, but also to the power supply systemthat provides power to the microcontroller and other elements of the SRSsystem.

For example, if there is a short circuit on a circuit board or otherpiece of electronic equipment that is associated with the SRS system,there is a possibility that the airbag may deploy under certainconditions when it should not. In another example, if power is removedfrom a circuit board or other piece of electronic equipment during anemergency situation, such as a collision, there is a possibility thatthe airbag may not deploy when it should. Thus, additional efforts areoften necessary when designing electronic circuits for automotive safetyapplications. For example, automotive functional safety requirements maybe specified in certain standards, such as ASEAL-D IS026262.

SUMMARY

According to an embodiment, a system includes a switching regulator andan electrochemical storage test circuit. The switching regulator iscoupled to a power supply input and configured to supply a regulatedvoltage to a regulated supply terminal that is configured to be coupledto a device. The electrochemical storage test circuit is configured tobe coupled to an electrochemical storage unit. The electrochemicalstorage test circuit includes a bidirectional switch with a first switchterminal coupled to the regulated supply terminal, a second switchterminal configured to be coupled to the electrochemical storage unit,and a switch control terminal. The electrochemical storage test circuitalso includes a built-in self-test (BIST) circuit configured to becoupled to the electrochemical storage unit and to the switch controlterminal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a system block diagram of an embodiment emergencybackup battery system;

FIG. 2 illustrates a schematic of an embodiment airbag system;

FIG. 3 illustrates a schematic of an embodiment backup battery built-inself-test (BIST);

FIG. 4 illustrates a flowchart diagram of an embodiment BIST method;

FIG. 5 illustrates a block diagram of an embodiment method of operation;and

FIG. 6 illustrates a block diagram of another embodiment method ofoperation.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the various embodimentsdescribed herein are applicable in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use various embodiments, and should not be construed ina limited scope.

Description is made with respect to various embodiments in a specificcontext, namely safety systems and, more particularly, automotive safetysystems. Some of the various embodiments described herein includeairbags, airbag firing and controls circuits, backup battery suppliesfor airbag systems and firing and control circuits, and built-inself-test (BIST) for backup battery and airbag systems. In otherembodiments, aspects may also be applied to other applications involvingany type of backup system or safety system according to any fashion asknown in the art.

According to an embodiment, airbag systems, sometimes referred to asairbag supplemental restraint systems (SRS), require a high level ofsafety during operation. Namely, the airbag system must activate duringappropriate circumstances, such as during a collision, and must notactivate during other circumstances, such as the closing of a door. Invarious situations, it is possible that the regular system battery, suchas an automotive battery, may be disconnected from the airbag system. Insuch situations, the airbag system is without power, yet must stillactivate in the case of a collision, for example. Often in suchsituations, the squibs for firing the airbags are supplied by a backupcapacitor or set of capacitors. According to various embodiments, thesquibs, or other safety system components, are powered by a backupbattery when the primary automotive battery is unavailable ordisconnected from the airbag system. In various other embodiments, thebackup battery may be used with various types of safety system toactivate safety or emergency components in the case of detection of anemergency or unsafe event. In various embodiments, the backup battery iscoupled to a built-in self-test (BIST) circuit in order to ensure properoperation during a collision or other emergency. The BIST circuit isconfigured to monitor the health of the battery and notify a person orsystem in the case of an error in the backup battery system.

FIG. 1 illustrates a system block diagram of an embodiment emergencybackup battery system 100 including switching regulator 102, control andBIST circuit 104, backup battery 106, switch 108, squib 110, buckconverter 112, microcontroller 114, and satellites 116. According tovarious embodiments, switching regulator 102 receives power from powersupply line PW and generates regulated voltage VREG at node 118.Switching regulator 102 may be implemented as a non-switching regulatorin alternative embodiments. Control and BIST circuit 104 generatesswitching control SWC for switch 108 such that during typical, ornon-emergency, operation switch 108 supplies power from switchingregulator 102 to backup battery 106 and other components within batterysystem 100. In various embodiments, control and BIST circuit 104 alsogenerates switching control SWC for switch 108 during an emergencyoperation, such as during an automotive collision, such that battery 106supplies power to squib 110, microcontroller 114, satellites 116, andother system components, for example. Additionally, during a testoperation, control and BIST 104 generates switching control SWC forswitch 108 in order to perform a self-test on backup battery 106 andensure correct operation of backup battery 106.

According to various embodiments, backup battery 106 is formed ofmultiple energy storage cells. In the embodiment shown, backup battery106 is formed of four cells. In other specific embodiments, backupbattery 106 is formed of three or five cells. In still otherembodiments, backup battery 106 may be formed of any number of cells.

Further, according to some embodiments, backup battery 106 is formed ofbattery cells that have high stability and a very long lifetime.Specifically, backup battery 106 may have a lifetime of 20 years,depending on charge cycling. Further, backup battery 106 may beimplemented such that the cells of the battery will not explode, such asduring extreme conditions or failure conditions, for example. In onespecific embodiment, backup battery 106 is formed of lithium ironphosphate (LiFePO₄) cells. In another specific embodiment, backupbattery 106 is formed of lithium titanate (Li₂TiO₃) cells. In otherembodiments, backup battery 106 may be implemented using other batterytypes or any other appropriate types of electrochemical storage cell.For example, backup battery 106 may be implemented using supercapacitorsor other equivalents.

According to various embodiments, squib 110 may contain numerous squibsfor firing one or multiple airbags. In other embodiments, squib 110 maybe replaced by any other emergency safety devices that are powered bybackup battery 106 during detected emergency events. Buck converter 112is an optional component for regulating and down converting regulatedvoltage VREG in order to supply microcontroller 114. In someembodiments, microcontroller 114 is implemented as a microcontroller,field programmable gate array (FPGA), or fully or partially customapplication specific integrated circuit (ASIC). In an alternativeembodiment, microcontroller 114 may be implemented with other equivalentcontrol circuits.

In various embodiments, satellites 116 include any number of sensors fordetecting an emergency event, such as an automotive collision forexample. In some embodiments, satellites 116 may include accelerometers,gyroscopes, pressure sensors, or other types of sensors for detecting acollision or other event. In specific embodiments, satellites 116 areimplemented as microelectromechanical systems (MEMS) sensors formedaccording to microfabrication techniques. For example, in someembodiments, all the components of backup battery system 100 may becontained in a single airbag module or unit. The circuit components,i.e., every component except squib 110, may be attached to a sameprinted circuit board (PCB). In some embodiments, satellites 116 aredistributed at various positions in a vehicle or structure in order todetect an emergency event, such as a collision.

According to specific embodiments related to airbag systems in anautomobile application, microcontroller 114 detects a collision based ondata received from satellites 116 and determines that firing one ormultiple airbags (not shown, coupled to squib or squibs 110) isnecessary. In such embodiments, microcontroller 114 controls squib 110to fire and also supplies control signals to close switch 108 andconnect backup battery 106 to squib 110. In various embodiments,microcontroller 114 may be coupled directly to switch 108, to anothercontrol unit, or to control and BIST 104 (connections not shown forsimplicity) in order to control switch 108 to close when activatingsquib 110. Further description of system components, operation, and theBIST is provided below in reference to the other figures.

FIG. 2 illustrates a schematic of an embodiment airbag system 200including buck-boost controller 202, safe switch control circuit 212,buck controller 214, low voltage regulator (LVR) control circuit 216,and voltage measurement and channel select circuit 218, among othercomponents. According to various embodiments, buck-boost controller 202controls switches 204 a, 204 b, 204 c, and 204 d in order to convert andregulate supply voltage VIGN and generate regulated voltage VREGtherefrom. Buck-boost controller 202 receives control information fromswitched mode power supply (SMPS) controller 210, which is alsoregulated by fault monitor 220. Regulated voltage VREG is supplied toswitch 108, to overcurrent limit circuit 222, to buck controller 214through logic safety switch 228, and as firing voltage VF to a squib orsquibs (not shown). BIST and control circuit 104 controls switch 108with switch control signal SWC and also tests backup battery 106, asdescribed further hereinabove in reference to FIG. 1 and herein below inreference to FIGS. 3-6.

In various embodiments, buck controller 214 generates buck voltage VBUCKfrom regulated voltage VREG by controlled switching of switches 230 aand 230 b, which are coupled to buck inductor LBK and buck capacitorCBK. Buck voltage VBUCK is a regulated voltage lower than regulatedvoltage VREG. In some embodiments, buck voltage VBUCK is supplied tovarious system components, such as microcontroller 114, as shown inFIG. 1. Additionally, buck voltage VBUCK is supplied to voltagemeasurement and channel select circuit 218 through internal LVR (iLVR)226. In an embodiment, iLVR 226 is integrated on a same semiconductordie with airbag system 200 and supplies a regulated voltage to internaldigital components. Voltage measurement and channel select circuit 218monitors input, output, and feedback signals throughout airbag system200 and supplies channel selection information and measurement data onserial peripheral interface (SPI) 238. In various embodiments, SPI 238is also coupled to wakeup control circuit 224, SMPS controller 210,buck-boost controller 202, overcurrent limit 222, logic safety controlcircuit 212, buck controller 214, and LVR control circuit 216 in orderto provide control status information between system components.

According to various embodiments, airbag system 200 is illustratedwithout various feedback signals and control signals in order to presentthe primary components and connections. In such embodiments, in additionto the illustrated signals, any control or regulation circuit mayinclude additional control connections and inputs as well as some typeof feedback connection coupled to an output node.

In various embodiments, internal regulators 206 receives input supplyvoltage VIGN from ignition filter 208, an oscillator signal fromoscillator 234, reference voltages from references circuit 236, and mainbattery voltage VBATT from a main battery coupling. Internal regulators206 supply all internal supplies needed to bias different analog anddigital domains used for startup and for operation.

According to some embodiments, switches 204 a-d are switched to chargeand discharge buck-boost inductor LBB and buck-boost capacitor CBB inorder to either buck or boost input supply voltage VIGN and generateregulated voltage VREG. In some embodiments, regulated voltage VREG maybe set to a storage voltage for backup battery 106 in order to increasethe lifespan of the battery. In particular embodiments, regulatedvoltage VREG may be between 10V and 15V. In other embodiments, regulatedvoltage VREG may be other voltages. In some embodiments, switch 108,which may be referred to as a bidirectional switch, is controlled tomaintain regulated voltage VREG on backup battery 106 during normal,non-emergency, operation as described hereinabove in reference to FIG.1.

According to some embodiments, regulated voltage VREG is also suppliedas satellite voltage VSAT to satellite sensors (not shown), such assatellites 116 in FIG. 1. Regulated voltage VREG is supplied assatellite voltage VSAT through overcurrent limit circuit 222, whichmonitors the supplied current and disconnects the satellites if anovercurrent is detected. Similarly, some embodiments include logicsafety control circuit 212 and logic safety switch 228 for protectingbuck controller 214 and limiting buck voltage VBUCK. In suchembodiments, logic safety control circuit 212 switches logic safetyswitch 228 if a voltage error condition is detected. Logic safetycontrol circuit 212 may include a charge pump for providing a boosteddrive voltage in order to drive logic safety switch 228 into an onstate. In some embodiments, logic safety switch 228 is implemented withan external DMOS transistor.

According to various embodiments, wakeup control circuit 224 may receivea wakeup signal (not shown) or detect a wakeup condition and provide astartup control sequence to the components in airbag system 200, such asSMPS controller 210, buck-boost controller 202, and buck controller 214,for example.

In some embodiments, LVR control circuit 216 receives an input voltageLVR_in, which may be coupled to or dependent on regulated voltage VREGor buck voltage VBUCK, and controls switch 232 based on input voltageLVR_in. Thus, LVR control circuit 216 and switch 232 together supply LVRvoltage VLVR, while LVR capacitor CLVR filters LVR voltage VLVR.

FIG. 3 illustrates a schematic of an embodiment backup battery built-inself-test (BIST) arrangement 250 including backup battery 106,bidirectional switch 108, and BIST circuit 104, which further includesmultiplexer 252, analog to digital converter (ADC) 254, controller 256,and controllable current source 258. According to various embodiments,BIST circuit 104 is configured to perform a self-test (BIST) on backupbattery 106 in order to ensure that the battery is operating correctly.Specific embodiment tests are described in relation to FIGS. 4 and 5herein below.

In various embodiments, multiplexer 252 is controlled by controller 256to select different voltage nodes of the battery or the input firingvoltage VF. In some embodiments, firing voltage VF may be the voltageused to activate the squib or squibs for firing an airbag or airbags, asan example. As described above in reference to FIGS. 1 and 2, firingvoltage VF may be equal to regulated voltage VREG. ADC 254 receives theselected voltage and converts the analog signal to a digital value thatis received at controller 256, which determines if backup battery 106and firing voltage VF are within normal operation limits. For example,in some embodiments, the internal resistance of backup battery 106 andthe voltage on each battery cell is determined within controller 256during a self-test. In various embodiments, controller 256 generatescontrol signals for controllable current switch 258, which sinksdischarge current IDIS, and also for bidirectional switch 108. During aself-test, controllable current switch 258 and bidirectional switch 108may be controlled according to the specific embodiment test implemented,as described below in reference to FIGS. 4 and 5.

In an embodiment, controller 256 within BIST circuit 104 is coupled toerror notification unit 260, which manages errors and notifies the useror operator in case of an error detected during a self-test by BISTcircuit 104. Controller 256 may be implemented as custom digital logic,such as with an FPGA or ASIC. In alternative embodiments, controller 256may be implemented with a microcontroller. In such embodiments,multiplexer 252 and ADC 254 may be included within the microcontroller.

FIG. 4 illustrates a flowchart diagram of an embodiment BIST method 300including blocks 302-332, which may be implemented by BIST arrangement250. According to an embodiment, block 302 includes reading or measuringfiring voltage VF. Based on the measuring in block 302, block 304 checksif firing voltage VF is valid by determining if firing voltage VF iswithin a designed threshold range. For example, the target firingvoltage may be 10V and the threshold range may be +/−2V leading to athreshold range of 8-12V. Some embodiments may include larger or smallerthreshold ranges and may be centered at other target firing voltages. Iffiring voltage VF is within the threshold range, block 304 identifiesfiring voltage VF as valid and proceeds to block 308 to set switchingcontrol SWC to an ON level. If firing voltage VF is not within thethreshold range, block 304 identifies firing voltage VF as invalid andproceeds to block 306 to set or maintain switching control SWC to an OFFlevel and signal a fault condition.

According to an embodiment, block 310 includes setting or maintainingcontrollable current source 258 in an OFF state and, thereby, generatingor sinking zero discharge current. Block 312 includes measuring, in afirst instance, voltages on the storage cells of backup battery 106. Insome embodiments, the measurements may be designated V1C1, V1C2, . . . ,and V1Cn, where n is the number of cells, C1-Cn indicates the specificcell, and V1 indicates voltages measured in the first instance ormeasuring. Following the first series of voltage measurements on thecells of backup battery 106, block 314 includes setting controllablecurrent source 258 in an ON state and, thereby, generating or sinkingdischarge current IDIS.

In an embodiment, block 316 includes measuring, in a second instance,voltages on the storage cells of backup battery 106. In someembodiments, the measurements may be designated V2C1, V2C2, . . . , andV2Cn, where n again is the number of cells, C1-Cn indicates the specificcell, and V2 indicates voltages measured in the second instance ormeasuring. After block 316, block 318 includes waiting a delay timet_(delay). In specific embodiments, delay time t_(delay) may be set tobetween about 1 ms and about 1000 ms. In further embodiments, delay timet_(delay) may be set by dividing the desired battery capacity bydischarge current IDIS. For example, if the battery capacity is 12 μAh(0.012 mAh), corresponding to 12 squibs using 1 μAh each, and currentsource 258 has discharge current IDIS equal to 100 mA, then delay timet_(delay) may be set equal to 0.012 mAh÷ 100 mA, which equals 0.00012hours, or 432 ms. In other embodiments, delay time t_(delay) may be anyvalue. After waiting delay time t_(delay), block 320 includes settingcontrollable current source 258 back in the OFF state and againgenerating or sinking zero discharge current.

According to an embodiment, block 322 includes measuring, in a thirdinstance, voltages on the storage cells of backup battery 106. In someembodiments, the measurements may be designated V3C1, V3C2, . . . , andV3Cn, where n again is the number of cells, C1-Cn indicates the specificcell, and V3 indicates voltages measured in the third instance ormeasuring.

Following the third series of measurements in block 322, block 324includes checking that the capacity of backup battery 106 meets aminimum capacity for activating a safety device, such as firing a squibor multiple squibs in some embodiments. In a specific embodiment, aminimum energy storage for backup battery 106 may be 1 microampere hour(μAh) per squib. This minimum energy storage, for example, is based on amaximum firing current for a squib of 1.52 A for a duration of 2.1 ms,leading to roughly 1 μAh being required to fire a squib. Thus, in aspecific embodiment using 12 squibs to fire an airbag or set of airbags,backup battery 106 requires 12 μAh as a minimum capacity. In otherembodiments, different safety devices or different squib requirementsdetermine a different minimum capacity for backup battery 106 and BISTmethod 300 may be modified accordingly. Thus, according to anembodiment, block 324 may check that backup battery 106 is able tosupply discharge current IDIS for the full duration of delay timet_(delay) and may also check that the voltages V3C1 . . . V3Cn are eachabove a minimum voltage indicating that backup battery 106 hasmaintained the minimum capacity. If it is determined in block 324 thatbackup battery 106 does not have the minimum capacity for activating thesafety device or devices, block 326 follows and includes signaling acapacity fault to a system error manager and the user, such as througherror notification unit 260 in FIG. 3. For example, block 326 mayinclude a warning light in an instrument panel of an automobile fornotifying the operator that the airbag system has an error.

In an embodiment, if it is determined in block 324 that backup battery106 does have the minimum capacity for activating the safety device ordevices, block 328 follows and includes checking that internalresistance RINT of backup battery 106 meets a required internal firingresistance RFIRE for activating the safety device. In a specificexample, as discussed above, each squib may require a current of 1.52 Ato activate or fire. In order to improve the safety margin, the minimumfiring current may be set to 2 A/squib in some embodiments. Thus, a 12squib system may require a current of 24 A. Accordingly, the maximumvalue for internal firing resistance RFIRE may be set between 0.1Ω and0.5Ω in specific embodiments in order to supply the minimum firingcurrent. In other embodiments, internal firing resistance RFIRE may beset outside this range, depending on the safety device or devices usedand the voltage and current required to activate the specific type ofsafety device.

In some embodiments, block 328 includes determining internal resistanceRINT_k of each cell of backup battery 106 according to the formulaRINT_k=(V1Ck−V2Ck)÷IDIS, where k is used to indicate a specific batterycell C1-Cn. In such embodiments, block 328 also includes checking thateach internal resistance RINT_k is less than or equal to the maximuminternal firing resistance RFIRE. If the internal resistance of eachcell of backup battery 106 is below internal firing resistance RFIRE,block 332 follows and indicates that backup battery 106 passes the BISTand is operating correctly. If, on the other hand, the internalresistance of each cell of backup battery 106 is not below internalfiring resistance RFIRE, block 330 follows and indicates that backupbattery 106 is not able to activate the safety device in the event of anemergency. Accordingly, block 330 includes signaling an internalresistance fault to the system error manager and the user, which mayinclude error notification unit 260 and activating a warning light in aninstrument panel, as similarly described in reference to block 326.

In various embodiments, blocks 302-332 of BIST method 300 may includeadditional steps or blocks and may also be rearranged according tovarious other sequences.

FIG. 5 illustrates a block diagram of an embodiment method of operation340 including steps 342-362. According to various embodiments, method ofoperation 340 may be an implementation of a further embodiment BISTmethod for testing an electrochemical storage unit, such as a backupbattery, coupled to an emergency safety device, such as a squib orsquibs for an airbag. In an embodiment, step 342 includes measuring afirst voltage on the electrochemical storage unit. Step 344 includesenabling a discharge current from the electrochemical storage unit.After enabling the discharge current, step 346 includes measuring asecond voltage on the electrochemical storage unit. Step 348 includeswaiting a delay time t_(delay). After delay time t_(delay), step 350includes disabling the discharge current.

According to an embodiment, step 352 includes measuring a third voltageon the battery after the discharge current is disabled. Next, step 354includes performing a first comparing of the third voltage to a capacitythreshold. Step 356 includes indicating a first error condition based onthe first comparing. Following steps 354 and 356, step 358 includesdetermining an internal resistance of the battery based on the firstvoltage, the second voltage, and the discharge current and step 360includes performing a second comparing of the internal resistance to aresistance threshold. Finally, step 362 includes indicating a seconderror condition based on the second comparing. In some embodiments, thebattery may be any type of electrochemical storage unit. In variousembodiments, additional steps may be included and the steps may befurther arranged according to other sequences in some alternativeembodiments.

FIG. 6 illustrates a block diagram of another embodiment method ofoperation 370 including steps 372-382. According to an embodiment,method of operation 370 is a method of operating an airbag system. Step372 includes regulating a received input power. Step 374 includessupplying the regulated input power to an electrochemical storage unitduring a first mode of operation. Step 376 includes performing abuilt-in self-test (BIST) for the electrochemical storage unit in asecond mode operation.

In an embodiment, step 378 includes detecting an activation event. Step380 includes entering a third mode of operation upon detecting theactivation event. Finally, step 382 includes supplying power to a squibfrom the electrochemical storage unit during the third mode ofoperation. In such an embodiment, the squib is configured to inflate theairbag when the squib is supplied from the electrochemical storage unit.According to further embodiments, multiple squibs may be supplied. In analternative embodiment, safety devices other than airbags and squibs maybe used and supplied. Steps 372-382 in method 370 may be arranged in adifferent sequence and may also include additional steps in alternativeembodiments.

According to an embodiment, a backup and supply safety system includes aswitching regulator and an electrochemical storage test circuit. Theswitching regulator is coupled to a power supply input and configured tosupply a regulated voltage to a regulated supply terminal that isconfigured to be coupled to a safety device. The electrochemical storagetest circuit is configured to be coupled to an electrochemical storageunit. The electrochemical storage test circuit includes a bidirectionalswitch with a first switch terminal coupled to the regulated supplyterminal, a second switch terminal configured to be coupled to theelectrochemical storage unit, and a switch control terminal. Theelectrochemical storage test circuit also includes a built-in self-test(BIST) circuit configured to be coupled to the electrochemical storageunit and to the switch control terminal.

In various embodiments, the backup and supply safety system furtherincludes the electrochemical storage unit. The electrochemical storageunit may be a battery. In such embodiments, the battery may include aplurality of storage cells. In some embodiments, the BIST circuitincludes a multiplexer with a plurality inputs and an output, ananalog-to-digital converter (ADC) coupled to the output of themultiplexer, a controllable current source coupled to the batterythrough the bidirectional switch, and a logic control circuit coupled tothe bidirectional switch, the controllable current source, themultiplexer, and the ADC. In such embodiments, each storage cell of thebattery is coupled to an input of the multiplexer. In some embodiments,the battery is a lithium iron phosphate battery or a lithium titanatebattery.

In various embodiments, the safety device is a squib configured toinflate an airbag. In some embodiments, the safety system is whollycontained within an airbag safety module. The switching regulator may bea full-bridge buck-boost switching regulator. In an embodiment, thebidirectional switch includes a first field effect transistor (FET) witha source, a drain coupled to the first switch terminal, and a gatecoupled to the switch control terminal, and a second field effecttransistor (FET) with a source coupled to the source of the first FET, adrain coupled to the second switch terminal, and a gate coupled to theswitch control terminal.

In various embodiments, the bidirectional switch is configured to supplypower from the switching regulator to the electrochemical storage unitduring a first mode and to supply power from the electrochemical storageunit to the safety device in a second mode. The first mode includesoperation of the safety system before detection of an event and thesecond mode includes operation of the safety system after detection ofthe event. The safety system may further include a microcontrollercoupled to the regulated supply terminal and configured to be coupled tothe safety device. The microcontroller controls the bidirectional switchto operate in the first mode or the second mode. In an embodiment, thesafety system further includes an accelerometer coupled to themicrocontroller and a pressure sensor coupled to the microcontroller. Insuch an embodiment, the microcontroller is configured to detect theevent based on inputs received from the accelerometer and the pressuresensor. In an embodiment, the safety system further includes a buckconverter coupled between the regulated supply terminal and themicrocontroller.

In various embodiments, the BIST circuit is configured to measure afirst voltage on the electrochemical storage unit, enable a dischargecurrent from the electrochemical storage unit, measure a second voltageon the electrochemical storage unit after the discharge current isenabled, wait a delay time, disable the discharge current after waitingthe delay time, measure a third voltage on the electrochemical storageunit after the discharge current is disabled, perform a first comparingof the third voltage to a capacity threshold, indicate a first errorcondition based on the first comparing, determine an internal resistanceof the electrochemical storage unit based on the first voltage, thesecond voltage, and the discharge current, perform a second comparing ofthe internal resistance to a resistance threshold, and indicate a seconderror condition based on the second comparing.

According to an embodiment, a method of operating a safety systemincludes regulating a received input power, supplying the regulatedinput power to an electrochemical storage unit during a first mode ofoperation, performing a built-in self-test (BIST) for theelectrochemical storage unit in a second mode of operation, detecting anactivation event, entering a third mode of operation upon detecting theactivation event, and supplying power to a safety device from theelectrochemical storage unit during the third mode of operation.

In various embodiments, the safety device includes a squib configured toinflate an airbag when the squib is supplied from the electrochemicalstorage unit. The electrochemical storage unit includes a lithium ironphosphate battery or a lithium titanate battery. In some embodiments,performing a BIST includes measuring a first voltage on theelectrochemical storage unit, enabling a discharge current from theelectrochemical storage unit, measuring a second voltage on theelectrochemical storage unit after the discharge current is enabled,waiting a delay time, disabling the discharge current after waiting thedelay time, measuring a third voltage on the electrochemical storageunit after the discharge current is disabled, performing a firstcomparing of the third voltage to a capacity threshold, indicating afirst error condition based on the first comparing, determining aninternal resistance of the electrochemical storage unit based on thefirst voltage, the second voltage, and the discharge current, performinga second comparing of the internal resistance to a resistance threshold,and indicating a second error condition based on the second comparing.

According to an embodiment, a method of testing a battery configured tobe coupled to a squib for an airbag includes measuring a first voltageon the battery, enabling a discharge current from the battery, measuringa second voltage on the battery after the discharge current is enabled,waiting a delay time, disabling the discharge current after waiting thedelay time, measuring a third voltage on the battery after the dischargecurrent is disabled, performing a first comparing of the third voltageto a capacity threshold, indicating a first error condition based on thefirst comparing, determining an internal resistance of the battery basedon the first voltage, the second voltage, and the discharge current,performing a second comparing of the internal resistance to a resistancethreshold, and indicating a second error condition based on the secondcomparing.

In various embodiments, the battery includes a plurality of storagecells and the method is performed for each cell of the plurality ofcells. The storage cell of the plurality of storage cells comprises alithium iron phosphate storage cell or a lithium titanate storage cell.

According to an embodiment, a test circuit includes a controllablecurrent source, a switch coupled to the controllable current source, abattery coupled to the switch, a plurality of voltage measurementcircuits, a multiplexer coupled to the plurality of measurementcircuits, an analog-to-digital converter (ADC) coupled to an output ofthe multiplexer, and a control circuit coupled to an output of the ADCand comprising a plurality of control connections. The battery includesa plurality of energy storage cells and each energy storage cell has afirst terminal and a second terminal. Further, each voltage measurementcircuit is coupled to the first terminal and the second terminal of anenergy storage cell of the plurality of energy storage cells. Theplurality of control connections are coupled to the controllable currentsource, the switch, the multiplexer, and the ADC.

In various embodiments, the test circuit further includes an errornotification unit coupled to the control circuit and configured tonotify a user operating a machine coupled to the battery. The batterymay be a lithium iron phosphate battery or a lithium titanate battery.

Advantages of various embodiments described herein may include replacinga high voltage capacitor as a backup supply for an emergency system witha long lifetime battery. The removal of the high voltage capacitor maydecrease cost in the energy storage unit and may also allow systemreorganization with lower voltage components being enabled by the longlifetime backup battery that provides a higher capacity at a lowervoltage as compared to a capacitor. Further advantages may includereduced power dissipation of the system along with reduced heatgeneration because of the reduced power dissipation. In some specificembodiments, a boost converter may be eliminated from specific safetysystems due to system redesign, resulting in reduced system costs.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. An backup and supply safety system, the safetysystem comprising: a switching regulator coupled to a power supply inputand configured to supply a regulated voltage to a regulated supplyterminal, the regulated supply terminal configured to be coupled to asafety device; and an electrochemical storage test circuit configured tobe coupled to an electrochemical storage unit, the electrochemicalstorage test circuit comprising: a bidirectional switch comprising afirst switch terminal coupled to the regulated supply terminal, a secondswitch terminal configured to be coupled to the electrochemical storageunit, and a switch control terminal, and a built-in self-test (BIST)circuit configured to be coupled to the electrochemical storage unit andto the switch control terminal.
 2. The safety system of claim 1, furthercomprising the electrochemical storage unit.
 3. The safety system ofclaim 2, wherein the electrochemical storage unit comprises a battery.4. The safety system of claim 3, wherein the battery comprises aplurality of storage cells.
 5. The safety system of claim 4, wherein theBIST circuit comprises: a multiplexer comprising a plurality inputs andan output, wherein each storage cell of the battery is coupled to aninput; an analog-to-digital converter (ADC) coupled to the output of themultiplexer; a controllable current source coupled to the batterythrough the bidirectional switch; and a logic control circuit coupled tothe bidirectional switch, the controllable current source, themultiplexer, and the ADC.
 6. The safety system of claim 3, wherein thebattery comprises a lithium iron phosphate battery or a lithium titanatebattery.
 7. The safety system of claim 1, wherein the safety devicecomprises a squib configured to inflate an airbag.
 8. The safety systemof claim 7, wherein the safety system is wholly contained within anairbag safety module.
 9. The safety system of claim 1, wherein theswitching regulator comprises a full-bridge buck-boost switchingregulator.
 10. The safety system of claim 1, wherein the bidirectionalswitch comprises: a first field effect transistor (FET) having a source,a drain coupled to the first switch terminal, and a gate coupled to theswitch control terminal; and a second field effect transistor (FET)having a source coupled to the source of the first FET, a drain coupledto the second switch terminal, and a gate coupled to the switch controlterminal.
 11. The safety system of claim 1, wherein the bidirectionalswitch is configured to supply power from the switching regulator to theelectrochemical storage unit during a first mode and to supply powerfrom the electrochemical storage unit to the safety device in a secondmode, wherein the first mode comprises operation of the safety systembefore detection of an event, and the second mode comprises operation ofthe safety system after detection of the event.
 12. The safety system ofclaim 11, further comprising a microcontroller coupled to the regulatedsupply terminal and configured to be coupled to the safety device,wherein the microcontroller controls the bidirectional switch to operatein the first mode or the second mode.
 13. The safety system of claim 12,further comprising: an accelerometer coupled to the microcontroller; anda pressure sensor coupled to the microcontroller, wherein themicrocontroller is configured to detect the event based on input fromthe accelerometer and from the pressure sensor.
 14. The safety system ofclaim 12, further comprising a buck converter coupled between theregulated supply terminal and the microcontroller.
 15. The safety systemof claim 1, wherein the BIST circuit is configured to: measure a firstvoltage on the electrochemical storage unit; enable a discharge currentfrom the electrochemical storage unit; measure a second voltage on theelectrochemical storage unit after the discharge current is enabled;wait a delay time; disable the discharge current after waiting the delaytime; measure a third voltage on the electrochemical storage unit afterthe discharge current is disabled; perform a first comparing of thethird voltage to a capacity threshold; indicate a first error conditionbased on the first comparing; determine an internal resistance of theelectrochemical storage unit based on the first voltage, the secondvoltage, and the discharge current; perform a second comparing of theinternal resistance to a resistance threshold; and indicate a seconderror condition based on the second comparing.
 16. A method of operatinga safety system, the method comprising: regulating a received inputpower; supplying the regulated input power to an electrochemical storageunit during a first mode of operation; performing a built-in self-test(BIST) for the electrochemical storage unit in a second mode ofoperation; detecting an activation event; entering a third mode ofoperation upon detecting the activation event; and supplying power to asafety device from the electrochemical storage unit during the thirdmode of operation.
 17. The method of claim 16, wherein the safety devicecomprises a squib configured to inflate an airbag when the squib issupplied from the electrochemical storage unit.
 18. The method of claim16, wherein the electrochemical storage unit comprises a lithium ironphosphate battery or a lithium titanate battery.
 19. The method of claim16, wherein performing a BIST comprises: measuring a first voltage onthe electrochemical storage unit; enabling a discharge current from theelectrochemical storage unit; measuring a second voltage on theelectrochemical storage unit after the discharge current is enabled;waiting a delay time; disabling the discharge current after waiting thedelay time; measuring a third voltage on the electrochemical storageunit after the discharge current is disabled; performing a firstcomparing of the third voltage to a capacity threshold; indicating afirst error condition based on the first comparing; determining aninternal resistance of the electrochemical storage unit based on thefirst voltage, the second voltage, and the discharge current; performinga second comparing of the internal resistance to a resistance threshold;and indicating a second error condition based on the second comparing.20. A method of testing a battery, the method comprising: measuring afirst voltage on the battery; enabling a discharge current from thebattery; measuring a second voltage on the battery after the dischargecurrent is enabled; waiting a delay time; disabling the dischargecurrent after waiting the delay time; measuring a third voltage on thebattery after the discharge current is disabled; performing a firstcomparing of the third voltage to a capacity threshold; indicating afirst error condition based on the first comparing; determining aninternal resistance of the battery based on the first voltage, thesecond voltage, and the discharge current; performing a second comparingof the internal resistance to a resistance threshold; and indicating asecond error condition based on the second comparing.
 21. The method ofclaim 20, wherein the battery comprises a plurality of storage cells andthe method is performed for each cell of the plurality of cells.
 22. Themethod of claim 21, wherein storage cell of the plurality of storagecells comprises a lithium iron phosphate storage cell or a lithiumtitanate storage cell.
 23. A test circuit comprising: a controllablecurrent source; a switch coupled to the controllable current source; aplurality of voltage measurement circuits, each voltage measurementcircuit configured to be coupled to a first terminal and a secondterminal of an energy storage cell of a plurality of energy storagecells; a multiplexer coupled to the plurality of voltage measurementcircuits; an analog-to-digital converter (ADC) coupled to an output ofthe multiplexer; and a control circuit coupled to an output of the ADCand comprising a plurality of control connections, wherein the pluralityof control connections are coupled to the controllable current source,the switch, the multiplexer, and the ADC.
 24. The test circuit of claim23, further comprising an error notification unit coupled to the controlcircuit and configured to notify a user of a battery error conditionbased on measurements by the plurality of voltage measurement circuits.25. The test circuit of claim 23, further comprising a battery coupledto the switch, the battery comprising the plurality of energy storagecells.
 26. The test circuit of claim 25, wherein the battery comprises alithium iron phosphate battery or a lithium titanate battery.